Effect of 2-(carboxyphenyl) retinamide and genistein on the formation of early lesions in 1,2-dimethylhydrazine-induced colon carcinogenesis in rats.

Aberrant crypt foci (ACF) are recognized as preneoplastic lesions for colon cancer, and ACF in rodents are widely used as an intermediate biomarker to predict tumorigenicity in the colon. However, a lack of correlations between the formation of ACF and the development of colonic tumors has been reported in several studies. For example, 2-(carboxyphenyl) retinamide (2-CPR) and genistein were reported to inhibit the carcinogen-induced formation of ACF, whereas both of them were later found to enhance colon tumorigenesis in rats treated with azoxymethane (AOM). Recently, we have identified b-catenin-accumulated crypts (BCAC) in the colon of rats shortly after administration of AOM, and provided evidence that these are independent early lesions of classical ACF, and BCAC might be direct precursors for colon cancers. In the present study, we performed a comparative analysis of the modifying effects of 2-CPR and genistein on 1,2-dimethylhydrazine (DMH)-induced BCAC and ACF in male F344 rats. Dietary administration of 2-CPR (315 ppm) significantly reduced the total number, multiplicity and size of ACF in DMH-exposed colonic mucosa, while genistein (250 ppm) had no significant effects on DMH-induced ACF formation. In contrast, both of 2-CPR and genistein significantly enhanced the multiplicity and size of DMH-induced BCAC when compared with DMH alone group. In addition, both 2-CPR and genistein significantly increased the proliferating cell nuclear antigen (PCNA) index preferentially in BCAC. Together with previous findings that 2-CPR and genistein are tumor promoters in the colon, our results support the concept that BCAC are precursors of colon tumors and suggest that these lesions are more reliable short-term biomarkers for colon carcinogenesis in rodents than ACF.

Preventive effects of a flavonoid myricitrin on the formation of azoxymethane-induced premalignant lesions in colons of rats.

The preventive effect of dietary exposure to a flavonoid myricitrin of azoxymethane (AOM)-induced aberrant crypt foci (ACF) and beta-catenin-accumulated crypts (BCAC) formation was investigated in male F344 rats. Thirty-four rats were divided randomly into five experimental groups. Rats in groups 1-3 were given subcutaneous injections of AOM (15 mg/kg body weight) once a week for 3 weeks. Starting 1 week before the first injection of AOM, rats in groups 2 and 3 were fed a diet containing 500 or 1000 ppm myricitrin, respectively, for 11 weeks. Rats in group 4 were fed a diet containing 1000 ppm myricitrin. Rats in groups 1 and 5 were given the basal diet alone during the study. The experiment was terminated 11 weeks after the start. The frequency of ACF per colon in group 3 treated with AOM and 1000 ppm myricitrin was significantly lower than that in group 1 treated with AOM alone (p<0.01). Furthermore, dietary myricitrin at both doses (groups 2 and 3) significantly inhibited the formation of BCAC when compared to group 1 (p<0.05). These results indicate that myricitrin had possible chemopreventive effects in the present short-term colon carcinogenesis bioassays and suggest that longer exposure may cause suppression of tumor development.